1. Field of the Invention
The present invention relates to a golf ball and more particularly to an improvement in a dimple of the golf ball.
2. Description of the Related Art
A golf ball has approximately 250 to 550 dimples on a surface thereof. The role of the dimples resides in one aspect that such dimples disturb an air flow around the golf ball during the flight of the golf ball to promote the transition of a turbulent flow on a boundary layer, thereby causing a turbulent flow separation (which will be hereinafter referred to as a xe2x80x9cdimple effectxe2x80x9d). The promotion of the transition of the turbulent flow causes a separating point of air from the golf ball to be shifted backwards so that a pressure resistance is reduced. Moreover, the promotion of the transition of the turbulent flow increases a difference between the upper and lower separating points of the golf ball which is caused by a backspin. Consequently, a lift acting on the golf ball is increased. A pressure resistance is reduced and the lift is enhanced so that the flight distance of the golf ball is increased. A dimple which easily promotes the transition of the turbulent flow, that is, a dimple capable of disturbing an air flow much better is aerodynamically excellent.
In order to obtain a golf ball having an excellent flight performance, there have been variously investigated a dimple volume (see Japanese Laid-Open Patent Publications Nos. 60-163674(U.S. Pat. No. 4,681,323) and 62-176465). At present, a large number of golf balls have the sum of dimple volumes (total volume) regulated to 480 mm3 to 620 mm3.
There has been variously investigated a surface area occupation ratio to be the ratio of a total area of dimples occupying the surface area of a virtual spherical surface (see Japanese Laid-Open Patent Publication No. 3-80876(U.S. Pat. No. 5,090,705)). At present, a large number of golf balls have the surface area occupation ratio regulated to 60% to 90%.
Furthermore, the planar and sectional shapes of the dimple, the number of dimples and an arrangement pattern have been variously improved in order to obtain a golf ball having an excellent flight performance.
The most important performance required for a golf ball by a golfer is a flight performance. The golf ball having an excellent flight performance gives a feeling of refreshing to the golfer, and furthermore, a score in a golf game can also be enhanced. While various improvements have been made for the dimple as described above, the golfer desires amore enhancement in the flight distance under actual circumstances.
The present invention has been made in consideration of such actual circumstances and has an object to provide a golf ball which has dimples improved and is therefore excellent in a flight performance.
In order to attain the object, the present invention provides a golf ball having a large number of dimples on a surface,
wherein when a volume of a region surrounded by a plane including edges of the dimples and surfaces of the dimples is represented by V1 and a volume of a region surrounded by the plane including the edges of the dimples and a virtual spherical surface is represented by V2, a ratio of the number of the dimples having the smaller volume V1 than the volume V2 to the total number of the dimples is 10% to 90%, and
a sum of the dimple volumes obtained by adding the volumes V1 and the volumes V2 is 480 mm3 to 620 mm3.
An ordinary golf ball employs a dimple having the greater volume V1 than the volume V2. On the other hand, the golf ball according to the present invention includes the dimple having the smaller volume V1 than the volume V2. The dimple having the smaller V1 than the volume V2 gives a small dimple volume for an area. The surface area of a virtual spherical surface is limited. Therefore, the golf ball including a dimple having the smaller volume V1 than the volume V2 and having a proper total dimple volume necessarily includes a dimple having the greater volume V1 than the volume V2 or both of them equal to each other. More specifically, the golf ball according to the present invention has both a dimple satisfying (V1 less than V2) and a dimple satisfying (V1xe2x89xa7V2). In the golf ball, the dimple satisfying (V1 less than V2) and a dimple satisfying (V1xe2x89xa7V2) appear in mixture by a backspin. Consequently, the effect of disturbing an air flow can be promoted. The golf ball has an excellent flight performance.
Preferably, a ratio (V2/V1) of the volume V2 to the volume V1 in the dimple having the smaller volume V1 than the volume V2 is 1.01 or more. Consequently, the effect of disturbing an air flow can be promoted still more.
Preferably, the golf ball includes a dimple having the smaller volume V1 than the volume V2 and a diameter of 3.8 mm or more. The dimple having a comparatively large diameter and satisfying (V1 less than V2) can promote the disturbance of the air flow still more. A ratio of the number of the dimples having the smaller volume V1 than the volume V2 and a diameter of 3.8 mm or more to the total number of the dimples is preferably 10% to 45%.
Preferably, the golf ball includes plural kinds of dimples having diameters different from each other and the smaller volume V1 than the volume V2. Consequently, the disturbance of the air flow can be promoted still more.
In the golf ball having a surface area occupation ratio of 60% to 90%, the effect of enhancing a flight performance by the mixture of the dimple satisfying (V1 less than V2) and the dimple satisfying (V1xe2x89xa7V2) is particularly remarkable.